This project previously established a model system to study the effects of killer lymphocytes on foreign cell membranes by using antibody coated planar lipid bilayers as target membranes for attack by normal human lymphocytes. To extend this project, Dr. Stephens has been measuring the electrical properties of target cell membranes using microelectrodes for intracellular recording. Complement mediated killing of these cells is accomplished by a dramatic and early loss of membrane potential and electrical resistance. Under some conditions cells can recover from this membrane damage and escape subsequent death. To obtain more detailed information on the nature of this membrane lesion, Dr. Simone has performed experiments using resealed red blood cell ghost membranes with fluorescent dextran molecules of varying defined sizes inside. These experiments show that complement lesions allow 40,000 molecular weight molecules to escape but not those of 80,000 mw, while antibody dependent lymphocyte mediated killing of these targets allows molecules of 500,000 but not 2,000,000 molecular weight to escape. Thus we can define a discrete sized pore in the membrane after damage to the target cell, confirming the concept that killer lymphocytes operate by this mechanism.